Angiotensin II (5-8) is an endogenous C-terminal fragment of the peptide vasoconstrictor angiotensin II .¹It inhibits renin release from rat kidney slices at a concentration of 50 μM and relaxes rat aorta pre-contracted with phenylephrine .^2,1In vivo, microinjection of angiotensin II (5-8) into the ventrolateral periaqueductal gray (vlPAG) of rats increases mean arterial pressure (MAP) and decreases heart rate (HR) by approximately 2.7- and 3-fold less, respectively, than angiotensin II.¹It increases the latency to withdrawal in a tail-flick test and the mechanical withdrawal threshold in an incision allodynia test in rats when administered at a dose of 0.2 nmol into the vlPAG. Angiotensin II (5-8) (0.4 nmol, vlPAG microinjection) reduces the number of entries and time spent in the open arms of the elevated plus maze and increases the mean startle amplitude, a measure of conditioned fear, in response to foot shock.³

1.Guethe, L.M., Pelegrini-da-Silva, A., Borelli, K.G., et al.Angiotensin (5-8) modulates nociception at the rat periaqueductal gray via the NO-sGC pathway and an endogenous opioidNeuroscience231315-327(2013) 2.Naftilan, A.J., and Oparil, S.Inhibition of renin release from rat kidney slices by the angiotensinsAm. J. Physiol.235(1)F62-F68(1978) 3.Genaro, K., Juilano, M.A., Prado, W.A., et al.Effects of angiotensin (5-8) microinfusions into the ventrolateral periaqueductal gray on defensive behaviors in ratsBehav. Brain Res.256537-544(2013)